Solid propellants (fuels) are widely used in missile engines. The burning of the fuels generates a huge thrust so that a missile can be quickly launched. The main chemical compositions of solid fuels include nitrate (NO2), carbon (C) and sulfur (S). Such fuels are usually stored in the back portion of the missile for effectively generating the thrust.
During the long storage process of the missile (e.g., years), the compositions of the fuels can change due to the slow chemical reaction processes among different components of the fuels as well as the reactions of the fuels with the outside atmosphere (e.g., O2). Thus, to ensure a successful and safe launch of the missile, it is critical to be able to monitor the status of the fuels and ensure a proper fuel composition ratio at the time of use.